1. Field of the Invention
This invention relates to a tappet turning-prevention structure for a fuel supply apparatus for supplying fuel to a fuel injector in a cylinder injection type engine.
2. Description of the Related Art
FIG. 7 is a schematic view of a conventional fuel supply apparatus. In FIG. 7, a fuel supply apparatus 1 is arranged to be fitted in an unillustrated housing or the like of an engine, and is driven via a cam 28 that rotates at half rotational speed of the engine. A casing 2 of the fuel supply apparatus 1 is provided with unillustrated suction pipe and discharge pipe disposed therein. In addition, a cylindrical concaved housing section 3 is formed in the fuel supply apparatus in the downward section in FIG. 7.
A sleeve 5 having a cylinder section 4 is disposed within the concaved housing section 3. The sleeve 5 is disposed in the manner in which one end thereof faces toward a bottom 3a of the concaved housing section 3. The sleeve 5 comprises the hollow cylindrical cylinder section 4, a thick section 6 being formed by thickening a part of a bottom 4a of the cylinder section 4, and a securing section 8 being formed into the shape of a flange at the edge of the bottom 4a of the cylinder section 4.
A substantially cylinder-shaped piston 9 is disposed within the cylinder section 4 of the sleeve 5 in a way allowing its reciprocating motion. The piston 9 comprises a fuel pressurizing chamber 10 together with the cylinder section 4. A compression coil spring 11 is compressedly housed within the fuel pressurizing chamber 10. The compression coil spring 11 is held in place by a spring holder 12.
Disposed around the sleeve 5 is a housing 13 surrounding the sleeve 5. The housing 13 having the form of a substantially bottomless cup is provided with a cylinder-shaped flange section 13a at the outer circumference thereof. A holder 14 is fastened to the piston 9 at the end opposite to the side where the fuel pressurizing chamber 10 is formed. Bellows 15 made of metal are disposed between the housing 13 and the holder 14. The bellows 15 serve as a receptacle for fuel leaking out of the space between the piston 9 and the sleeve 5.
A tappet 16, or a driving member, having the form of a bottomed cylinder is abutted against the piston 9 at the end opposite to the side where the fuel pressurizing chamber 10 is formed. The tappet 16 comprises a cam roller 18 rotatably supported by a roller-supporting pin 17. The cam roller 18 is brought into contact with the cam surface of the cam 28. A spring holder 19 is fastened to the tappet 16, and a compression coil spring 20 is compressively mounted in a space between the spring holder 19 and the housing 13.
A bracket 21 is disposed around the compression coil spring 20 for the purpose of fastening the fuel supply pump 1 to an unillustrated housing and the like of an engine. The bracket 21 is substantially cylinder-shaped and has a flange section 21a formed therein at about half its height. The flange section 21a is provided with a plurality of unillustrated holes that pierce the flange section and are formed along its circumference at predetermined positions. The casing 2 is provided with unillustrated internally threaded holes in the positions corresponding to the unillustrated through holes. Bolts are inserted in the unillustrated through holes and are fastened to the unillustrated internal threaded holes. Thus, the bracket 21 is firmly attached to the casing 2. With the outer circumference of the bracket 21 being supported, the fuel supply pump 1 is fastened to an unillustrated housing and the like of an engine.
In a high-pressure fuel supply pump thus composed, piston 9 is pushed toward the tappet 16 by the compression coil spring 11. The tappet 16 on the other hand is pushed by the compression coil spring 20 so that it is always in contact with the cam 28. Thus, upon receiving force generated by the rotations of the cam 28, the piston 9 reciprocates within the cylindrical section 4.
In a conventional fuel supply apparatus having a construction as above described, as shown in FIGS. 7 and 8, the tappet 16 that faces toward the rotating cam 28 when the fuel supply pump is mounted to the housing or the like of the unillustrated engine and that is provided with the cam roller 18 driven by the cam 28 and transmits the motion of the cam 28 to the piston 9, and the arrangement for preventing the tappet 16 from turning about the axis of the piston is such that the pin 25 press-fitted into the outer circumference surface of the tappet 16 is brought into a loose engagement with a groove formed in the inner surface of the bracket 21 accommodating the tappet 16.
In the tappet turning prevention structure in a fuel supply apparatus having a construction as above described, however, the tappet 16 is provided with the pin 25 press-fitted in the outer circumference of the tappet 16 and a roller supporting pin 17 as functionally separate parts, and so both the process for press-fitting the pin 25 into the outer circumference of the tappet 16 and the process for positioning the cam roller 18 and the roller-supporting pin 17 in relation to the tappet 16 by a snap ring 27 that fits in both the inside slot formed within the tappet 16 and the outside slot formed at the outer circumference of the roller supporting pin 17 are involved in the tappet 16 assembly process.
Because the tappet 16 is provided with both the roller supporting pin 17 and the pin 25 press-fit in the outer circumference of the tappet 16, the number of parts is not small. In addition, because a slot into which the tappet turning-prevention pin 25 is press-fitted must be formed in the tappet 16, the number of processing stages is increased. Further, it is necessary to control the pressure load during the press-fitting the pin 25 into the outer circumference of the tappet 16 for the purpose of eliminating the deformation of the tappet 16.
Furthermore, because the pin 25 press-fit into the outer circumference of the tappet 16 and the roller supporting pin 17 are at right angles to each other within the tappet 16, the tappet 16 can be assembled only from a certain limited direction due to the shape of the bracket.
The present invention has been made to solve the problems discussed above and has as its object the provision of a tappet turning prevention structure in a fuel supply apparatus that requires lesser numbers of parts, part processing stages and items to be controlled in the assembly process and provides a larger degree of freedom of part assembling in the assembly process.
With the above object in view, the present invention resides in the tappet turning prevention structure in a fuel supply apparatus that comprises a piston disposed within the cylindrical section in a manner allowing its reciprocating motion and defining a fuel pressurizing chamber together with the cylindrical section. A tappet is disposed at one end of the piston opposite to the fuel pressurizing chamber and having accommodated therein a roller driven by a cam of an engine and a roller supporting pin for rotatably supporting the roller for transmitting a force of the cam to the piston. The tappet is housed by a bracket fastened to the casing for allowing a reciprocating motion, and the bracket has a groove in an inner surface thereof for allowing an end portion of the roller supporting pin to engage therein.
Thus, the number of parts can be decreased because the turning prevention pin for the tappet and the roller supporting pin have been integrated as a single common part, and therefore the need of controlling of the press-fit loads is eliminated because no process for thrusting the tappet turning prevention pin into the outer circumference of the tappet is involved.
The bracket may have two grooves in an inner surface thereof for allowing the roller supporting pin is engaged by the grooves at both opposing end.